On a mission to a newly discovered planet, an astronaut finds copper abundances of 69.97 % for 63cu and 31.03 % for 65cu. what is the atomic mass of copper for this location? the mass of 63cu is 62.9300 amu . the mass of 65cu is 64.9200 amu . express your answer to two decimal places, and include the appropriate units.

Okay so to find the average atomic mass of copper in this location, you want to take the percentage of  abundance of an isotope and multiply (in decimal form) that by it's atomic mass, then you would add that with the product of the % of abundance of the other isotope times it's atomic mass.

(Side Note: Isotopes are  atoms of the element that have the SAME number of protons  but different number of neutrons, so they have different mass numbers. Also average atomic mass is the average of all the isotopes in an element - this number is the one that is shown on the periodic table of elements, not mass number).

Let me show you how to do this..

For the isoptope 63Cu I will first need to convert it's percentage of abundance into a decimal, because we don't use the percentage to multiply. 69.97% -> 0.6997. Now I am going to take it's atomic mass 62.9300 and multiply that by 0.6997.

62.9300*0.6997=44.0321

Now we still need to find calculate this  for the isotope 65Cu. To convert 31.03% to a decimal I will just move the decimal point two places to the left, to get 0.3103.
So I am going to take this and multiply it by 64.9200 the atomic mass of the isotope 65Cu.

64.9200*0.3103=20.1447

Add the two of these to get the average atomic mass..
20.1447 + 44.0321=64.1768

What are the choices?